Recently, non-ferromagnetic amorphous steels based on Fe—Mn—Cr—Mo—C—B and Fe—(Mn, Cr)-(Ln, Y)—Mo—C—B (Ln=Lanthanides) bulk metallic glass (BMG), known as DARVA-Glass 1 and DARVA-Glass 101, respectively, have been reported (DARVA is abbreviation for DARPA-University of VIRGINIA; See International Patent Application Serial No. PCT/US03/04049, filed Feb. 11, 2003, entitled “BULK-SOLIDIFYING HIGH MANGANESE NON-FERROMAGNETIC AMORPHOUS STEEL ALLOYS AND RELATED METHOD OF USING AND MAKING THE SAME,” and corresponding U.S. application Ser. No. 10/364,123, filed Feb. 11, 2003, and International Patent Application Serial No. PCT/US2004/016442, filed May 25, 2004, entitled “NON-FERROMAGNETIC AMORPHOUS STEEL ALLOYS CONTAINING LARGE-ATOM METALS,” and corresponding U.S. application Ser. No. 10/559,002, filed Nov. 30, 2005, of which all of their respective disclosures are hereby incorporated by reference herein in their entirety [1, 2, 3]. DARVA-Glass 101 exhibits highly glass forming ability, and samples with diameter thicknesses of 12 mm can be obtained by copper mold injection casting. Hereafter, DARVA-Glass 1 and -Glass 101 will be called DVG 1 and DVG 101. Separately, another research group has produced similar Fe-based metallic glasses based on the results reported in reference no. 1, and therefore compositions similar to DVG 101 [4] The fracture yield strengths of amorphous steels are found to be three times those of high-strength stainless steel alloys, and their elastic moduli observed in the range 150-200 GPa are comparable to super-austenitic steels. Furthermore, in the supercooled liquid regions, amorphous steels can be bent into various configurations by hand or compressed by as much as 40% under a pressure of only 20% of the fracture strength. The high processability and high mechanical strengths coupled with good corrosion resistance properties and superplastic behavior suggest that DVG amorphous steels can potentially be developed as formable non-ferromagnetic amorphous steel alloys [1, 2, 3]. The present amorphous steel compositional spreads reported in PCT/US03/04049 and PCT/US2004/016442 have included those regions that result in brittle as well as ductile samples, with measured or estimated fracture toughness ranging from 4.0 MPa-m [1, 2, 5] to above 10 MPa-m1/2. Prior to utilizing amorphous steels as structural materials, one must first improve the toughness of these DVG steels so that they will have a higher resistance to fracture.
In the 1980s', metallic-glass composites were synthesized by rapidly solidifying glass-forming melts embedded with ceramic particulate matter, and also by laminating thin amorphous metal layers with sheets of metal matrix (see referenced patents). Recently, BMG composites using ductile dendrites and hard particulates as reinforcements had been developed [6-14]. In addition to the two-phase BMG composites that were formed in more ductile Zr-based BMG, BMG composites were also developed for brittle monolithic BMG, such as the Mg-based BMG [13, 14]. The plastic deformation in monolithic BMG tends to be localized in narrow regions called shear bands, which under stress, will lead to unconstrained propagation of the shear bands, resulting in catastrophic material failure. The enhanced plastic strain to failure, or toughness, reported was attributed to impediment of run-away shear bands as well as formation of multiple shear bands in the presence of ductile crystalline phases or hard particulate matters. As a result, any further deformation will take place through the occurrence of shear bands elsewhere in the sample and the elongation is greatly improved. In some BMG forming alloys, two-phase crystalline microstructures consisting of ductile Zr—Ti-based, phases were formed in-situ in the bulk metallic glass matrix via chemical partitioning in the melt and primary dendritic growth [7-9]. Meanwhile, other BMG were found to devitrify to form composites that contain embedded crystalline or quasicrystalline particles [10-12]. In yet another method of forming BMG composites, a master alloy ingot with the glass forming composition was combined with metal or ceramic particles and induction melted to form the composite ingot, followed by casting to form BMG composite samples [6, 13, 14]. A significant increase in the plastic strain to failure ranging from ˜1 to more than 15% was demonstrated, while the corresponding monolithic BMG exhibited only 0 to 1% plastic strain [6-11, and 13, 14].
As for the DVG amorphous steels, although carbides and borides are formed at high temperatures, ductile austenitic phase has not been obtained. Meanwhile, there are reasons to believe that amorphous steels can be reinforced with hard ceramic particles to form a more ductile product. In designing amorphous steel composites, ceramic particulates with Vickers hardness and stiffness significantly larger than those of amorphous steels are selected (Table I). However, due to the high liquidus temperature (near 1200° C.) and high viscosity of the DVG liquids, previous approach of melting mixtures of master alloy ingots and ceramic particles is inadequate for producing samples with uniformly distributed embedded particulates without compromising the glass-forming composition.
An aspect of various embodiments of the present invention provides, among other things, practical methodologies that can be successfully applied to produce DVG amorphous steel composites with enhanced mechanical properties and ductility.